Control system



Feb. 2, 1937. WHITE 2,069,51o

CONTROL SYSTEM Filed Aug. 51, 1935 5 Sheets-Sheet l Hai- U v I v WITNESSES: IN VENTOR Feb; 2 1937. K. M. WHlTE 9 5 CONTROL SYSTEM Filed Aug. 31, 1935 3 Sheets-Sheet 3 .D X U I I i WITNESSES: Rd INVENTOR mbi Kemer/2 MPV/2176.

ATTO EY Patented Feb. 1937 CONTROL SYSTEM Kenneth M. White, Tenafly, N. J., assignor to Westinghose Electric Elevator Chicago, Ill., a corporation of Illlnois.

Application August 13, 1935, Serial No. 38,771

15 Claims. (Cl. 172-239) My invention relates, generally, to electric control systems, and it has particularly relation to control systems of the ward-Leonard type.

Control systems of the ward-Leonard type have many applications in which they are employed under widely varying conditions. In particular, when a system of this type is employed for controlling the operation of an elevator car a wide range of Operating conditions is met. It is not only necessary to move the elevator car upwardly in the hatchway or shaft, but it is also necessary to permitit to move downwardly, both under widely varying load and other conditions.

In controlling the operation of an elevator car with a ward-Leonard system a. motor is provided which is arranged to be mechanically connected to the elevator car by cables for moving the elevator car in both directions. Ordinarily, the motor is provided with a separately excited field winding and the desired direction of movement of the car effected by reversing the polarity applied to its armature. The motor is arranged to be energizd from a generator which may be provided'with a and suitable control devices for inserting various steps of the resistor. in circuit with-the main field winding. For each step of the controller which alters the current flowing through the main field winding of the gene'rator there is a particular speed of operation of the motor which is desired. Any departure in speedirom this desired value introduces undesirable Operating conditions in the I functioning of the system.

If it were possible to maintain all of the conditions in a 'control system of the ward-Leonard'` type absolutely constant, it would then be possible t'o obtain an exact relationship between the speed of the motor and the setting of the controller which regulates the flow of current through the main field winding of 'the generator. Due to the physical constants and characteristics of the system, however, it is not possible to achieve such a. result without the use of a compensating system of some type. This is particularly true When the ward-Leonard control system is employed to control the movement of an elevator car in a hatchway. In such case, additional variables enter into the functioning of the system which make it diflicult to maintain the speed of the elevator car 5 under all conditions in correspondence to the setting of the controller for the main field winding of the generator.

In connection with the elevator car itself, it operates under two extremes of conditions, that is, full load up and full load down. When the elevator car is operated with full load in theup direction, the motor has applied thereto maximum power fromthe generator. Under these conditions, it is necessary for the load to be lifted against the force of gravity. When the elevator car is Operating in the down direction under full load, the functioning of the motor is reversed and it operates as a generator to cause the generator to function as a motor and to return power to the power source in the event that the generator is arranged to be driven by means of a motor such as an alternating-current 'moton A further variable factor which enters into the iunctioning of the elevator car is the friction which it encounters in its movement along the hatchway.

When the elevator car is first installed, this triction may be relatively great but it lessens in eflect as the car is used-over a period of time.

'In the'motor which is connected to drive the elevator car various changes in its Operating conditions occur which aifect its speed. The resistance losses of the motor due to changes in j temperature constitute' one item of variation.

`These changes may be due, in part, to changes in temperature caused by changes in the weather' and, in part, by the loading oi the motor. That 'is,in the winter when it is cold the resistance losses of the motor will be somewhat less than heated to Operating temperature.

they are in the summer. Likewise, when the sys--` 0 tem is initiated in operation, the resistance losses are less than'they are when the system has been Operating and the motor has become Also depending upon the load carried by the motor, it will reach 4,'5 difierent Operating temperatures. A further variable in the operation of the motor comprises the change in resistance of its main field winding. Its resistance is changed in accordance with the temperature of the motor, and in accordance therewith, the .current flowing therethrough is somewhat altered to change the point on the magnetization curve of the motor at which it operates.

There are many conditions which aflect the 66 functioning of the generator that is connected to supply current to the motor. Since it operates under widely varying conditions, these results are particularly accentuated'. In order to reverse the direction of rotation of the motor, the current flowing through the main field winding of the generator is reversed. Depending upon the degree of reversal there is a change in the residual magnetism of the main poles, which, to a certain extent, will alter the' output of the generator for e the same setting of the controller. Furthermore,

the change in residual magnetism of the interpoles of the generator under these 'widely varying conditions also to a certain extent introduces another variable factor. The resistance of the main field winding of the generator' varies with temperature. 'As a result, for the same' setting of the controller, there may be different values of current flowing through it depending upon its temperature.

The condition of the commutator and brushe of the generator is another important variable commutator becomes grooved or roughened, due

to sand or other debris coming into contact with it and being carried underneath the brushes. When the system is subjected to heavy overloads, the brushholders tend to change their position tdue to the increase in temperature thereof caused by the overload. There is then a tendency for the brushes to be slightly shifted and as a result;

a cumulative or diiierential compounding efiect may be present, which introduces another variable factor. There is also some change in the contact drop across the faces o'f the brushes and through the brushes, due to current flow therethrough. This introduces still another variable factor.

In the crcult connecting the armatures of the motor and generator, it is necessary to introduce joints between the conductors. The contact resistance of these joints varies to some extent with the temperature caused by the weather and by the current flowing therethrough. As a result, there is some change in the resistance of the load circuit under these varying conditions.

Since all of the foregoing variable characteristics enter into the operation of a ward-Leonard control system employed for Operating an elevator car in a hatchway, it has been necessary in the v past to makecertain compromises in its functioning and to permit certain variations in the speed of the elevator car from the desiredspeeds. It has not been possible heretofore to operate the elevator car in the. hatchway at speeds corresponding to the setting of the controller of the main field winding of the generator, regardless of the load and Operating conditions of the system. As the system goes into service it has been neces- `sary in the past to continually make various adjustments in order to compensate for factors which change from time to time. As a result, the maintenance expense has been considerable and it has been necessary to provide a control system which is adjustable *over a comparatively wide range, in order to permit the necessary adjustaoeaso ments that were.required to be made from time to time.

In order to operate the elevator car so that under all conditions its movement will be' independent of all of the foregoing variable characteristics, it is desirable that the speed of the elevator car or the motor mechanically coupled thereto correspond precisely with the setting of the controller for the generator field winding, That is. regardless of these various !actors which variably aifect the functioning of the system, the speed of movement of the elevator car for each setting of the controller should be constant. regardless of the direction of movement of the elevator car. the load carried thereby, the temperature and operating conditions of the motor and generator, and other variable factors.

The object of my invention, generally stated, is

to provide a control system which shall be simple, efllcient and accurate in operation and which may 4 be readily and econom'ically manufactured and installed.

An important object of my invention is to provide for Operating the motor of a ward-Leonard control system at various constant speeds, regardless of variable charaoteristics of the system.

Another important object of my invention is to provide ior rendering the functioning oi' the motor of a ward-Leonard control system entirely independent of variable characteristics which might otherwise aifect the'functioning of the motor.

Another object of my invention is to provide for controlling the functioning of the generator of a ward-Leonard control system in accordance with the speed of the motor in such manner as to maintain the speed of the' motor at various predetermined values regardless of the variable Operating characteristics of the system. v

Still another object of my invention is to pro- -vide for controlling the functioningoi' the generator of a Ward-Leonard control system in accordance with departures of the speed of the motor from predetermined speeds and in accordance with the magnitude of the departures.

i v A further object of my invention is to provide a regulating generator having its armatureconnected in series 'circuit relation with the main generator field winding of a ward-Leonard control system and arranged to cause current to flow through the main generator fleldwinding in accordance with the current and voltage applied to the motor of the ward-Leonard system by the generator and the currentflowing through the main generator field winding.

A still further object of my invention is to provide a regulator generator having its armature connected in series circuit relation with the main' 'be responsive to the voltage applied to the motor,

and V a third field winding connected to be responsive to the current flowing through the main generator field winding.

Other objects of my invention wilt, in part, i

be obvious and, in part. appearhereinafter.-

My invention, accordingly, is disclosed in the embodiment hereof shown in the accompanying drawings, and comprises the features of construction, combination of elements and arrangement of parts which will be exemplifled in the construction hereinafter set for-th, .and the scope of the main' field winding o! the generator.

application of which will beindicated in the appended claims. i

For a more complete understanding ot'the natute' and scope of -my inventionyreference may be had to' the following detailed description. taken in connection with the accompanying drawings in which:

Figure 1 illustrates dagrammatically the arrangement of an elevator car in a hatchway;

Fig. 2 is a view, in side elevation, showing the construction of acontroller used tor varying the resistance connected 'in circuit with the main field winding ofthe' generator;

Fig. 3 is a view, partlyin side elevation and pa''tly in section, of a typical arrangement of the contact members ot the controller shown in Fig. 2;

`Fig. 4 illustrates diagrammatically one modification of my invention;

Fig. 4A shows the relationship between certain V Fig. 5 illustrat'es diagrammaticaliy another system in which'my invention may be employed;

a Fig. 5A illustrates the physical arrangement' of certain of the Operating windings and contact members of the relays and'switches iilustrated in Fig. 5;

Fig. 6 illustrates schematically the arrargement of the generatorarmature and main field winding; and n Fig. 7 illustrates 'schematicaliy the arrangement of the regulator-generator armature and' its field windings.

In order to practice my invention, a Ward Leonard control system is provided in which the motor is mechanically coupled as set forth hereinbefore to operate the elevator car in the hatchway. The motor is provided with a separatelyexcited field winding which is arranged to be energized in a single direction only. A generator is provided having its armature connected to the armature of the motor. The generator may be provided with a series field winding to comp'ensate for theIR drop 'in the armature circuits. The control of the speed of the motor, and consequently, of the elevator car, as well as the direction thereof, is controlled by' vary' lng the amount and direction ot the excitation of the This control may be effected in a few or many` steps, depending upon the type of operation which is desired.

In order to maintain the speed of the motor at various constant values corresponding to various settings of the controller used for controliing the current flowing through the main field winding of theggenerator, a regulator-generator is provided which is arranged to measure the speed and load of' the motor and the current flowing' through the main field winding of the generator. The armature of the regulator-generator is' arranged to be connected in series circuit relation y erator field winding which will be a function o! V the departure of the motor speed from a prede-. termined value corresponding to the particular setting of the controlier of the main field winding'. Under certain load and Operating conditions, no voltage will be generated in the armature o! the re'gulator-generator since, under these condi setting of the controlien For all other conditions, however, a voltage will be generated in the armature of the 'regulator-generator in such di-,

- to the motor, the regulator-generator is provided with a series field winding through which all or a portion of the current froni the generator 'flows. The regulator-generator is also provided with a main field winding which is connected to be responsive to the voltage applied to the motor. These two field windings are diiferentially related so that the resulting flux is a function of the speed of the motor, as measured by its counter E. M. F., that is, the flux generated bythe series field winding is proportional to the IR drop of the motor armature, and the flux generated by the main field winding of the regulator-generator is proportional to the voltage impressed across the terminals of the armature of the'motor. 'I'hus, the resulting flux due to the difierential relationship between the two `ileld windings, is a function of the counter E. M.`F. of the motor. Since this flux results from the combined action of the current flowing through the motor armafunction of the load carried by the motor. The

voltage whichis generated in the armature of the regulator-generator due to this resulting flux is then a function of the speed of the motor and the load carried thereby.

It is desirable that any change caused by the voltage generated in the regulator armature and affecting the current fiowing through the main field winding of the generator be immediately reflected in the voltage in the armature of the regulator generator. such action is desired in order to prevent hunting of the system. As soon as a voltage appears in the armature of the regul'ator-generator indicating that the-speed of the motor has departed from the desired speed, a change in the flow of current through the main field winding of the generator takes place in such direction as to tend to restorethe speed of the motor to the desired speed. If some means is not provided for 'immediately efiectlng a corresponding change in the corrective voltage generated in the armature of the regulator-generator, the resulting change in the fluxes of the series and main fleld windings of the regulator-generator in response to the corrective eflect will take place too late. As a result. the speed of the motor will be altered more than is desired and hunting will resuit. g

In order reguIator-generator proportional to the departure of the speed of the motor from the desired speed corresponding to a particular setting of the controller for the main field winding of the generator,

a diiferential field winding' is 'provided in the regulator-generator and is connected in series circuit relation with the mam field winding of the generator. Th's, any change in current which flows through the main generator field 'winding is immediately reflected in` the voltage *which is generated by the armature of the regulator-gener'ator. It is then unnecessary to await the correction in the speed ot the motor as reflected in the change in 'the fluxes generated. by the series and main field windings of the regulator-generator to cerrespondingly aflect the voltage generated by the i tions, the speed of the motor corresponds 'to the to make the correction applied by the the contact members El or E! come intoproxarmature of the regulator-generator. The differential. field winding of the regulator-generator is arranged to generate a flux in the same direction as the flux generated by th series field winding of the regulator-generator' and, therefore, it

'controller regardless of the many variable conditions which would otherwise aiIect the speed and cause it to change from the desired values.

Referring now particularly to Fig. 1 of the drawings, the reference character ill designates, generally, an elevator car which may be supported in a hatchway or shaft by means of a' cable Il which is passed over a sheave |2 and balanced by suitable counterweights 13. The elevator car ill is provided with a slowdown inductor relay E and a landing inductor -F. The slowdown inductor relay E is provided with normally closed contact members El and E! while the landing inductor F is provided with normally closed contact members FI .and F2. When the Operating winding of the slowdown inductor relay E is energized no action takes place until imity,`respectively, with the inductor plates UE and DE, depending upon the direction of travel of the elevator car. Assuming that the elevator car III is traveling in the up direction and that the Operating winding of the slowdown inductor relay E is energized, the contact members El will be opened as soon as they are moved into proximity to the inductor plate UE. A resulting control function then takes place which will be set forth hereinafter; The contact members FI and F! of the landing inductor relay F are also opened when they come into proximity, respectively, to the inductor plates UF and DF. ;The elevator car III is also provided with a master switch MS having three positions, the extreme outer positions corre'sponding to up and down movement of the car, and the central position to a position to stop the car.

In order to operate the elevator car I Il in'the hatchway, a" ward-Leonard control system is provided which comprises a motor M that is arranged to be mechanically coupled, as illustrated, to the sheave l2. `As shown in Fig, 4 of the drawings, the motor ;M comprises an armature Ma and a main field winding MI, the latter being ararmature Ge of the generator G 'is arranged to be mounted on a shaft I 4 which may be driven by any suitable motive'means, such as an induction motor (not shown) that may be con-' aoeaso shalt Il. As shown in Fig. "I of the drawlngs, the regulator generator R is provided with a main field winding Ri, a diflferential field winding Rd .and a series field winding Rs. As indicatedby the arrows, the differential field winding Rd and the series field winding Rs are arranged to generate fluxes'in a direction opposite to the direction of the flux generated by the main field winding R! of the regulator-generator. The particular connections tor the various field windings and the armature of the regulator-generator R are iliustrated in Figs. 4 and 5 of the drawings, and they win be set forth in detail hereinafter.

In response to the operation or themaster switch Ms. up or down reversing switches U and D are operated. On the operation of either of the up or down switches, an auxiliary switch X is operated to complete a circuit -for energizing the Operating windings of the inductor relays E 'and F.

As soon as either the up or the down switch U or D is operated, a' potentiometer PI is connected across the conductors Ll and L2. The current flowing through the potentiometer PI is in one direction when the up reversing switch U is energized. andis in a reverse direction when the down reversing switch D is energized.

In order to accelerate the motor M, the current flowing through the main generator field winding Gj is increased by increasing the voltage applied thereto from the potentiometer PI. This voltage' is gradually increased by the successive closure of contact members CI through cs, which as shown in Figs. 2 and 3 of the drawings, are arranged to be successively closed by means of a control motor CM. The control motor CM is arranged to operate through a reduction gearing mechanism |5 to fotate a shaft IS on which a series of cams l'i, composed of insulating' material, is mounted. As shown more clearly in Fig. 3 of the drawings, a cam l'i is arranged to engage aroller s on the periphery thereof and to normally hold a movable contact member !9 out of engagement with a fixed contact member 20. The cam ll is provided with a recessed portion z which is arranged to permit the roller a to move under the influence of a biasing spring 22, so that the movable contact member I!! is permitted to engage the fixed contact member 20. It will be understood that the cams l'l may be positioned on the shaft IS in any desired relative positions to eiTect. the sequential opening and closing of the contact ,members Ci through Ca, as may be desired. In order to stop the operation of the control motor CM after it has reached its limit of travel, contact members CS and CI !I are provided. The contact members CII are arranged to remain in the closed ;position until the control motor has reached its limit oi travel after being initially energized. At this time contact members CID are opened to terminate further motion of control motor CM in this direction, contact .members .cs having been closed on the energization o! the motor i CM. The contact members 09 are arranged to remain in the closed `position until the 'control motor CM has been restored to the initial position, at which time they are opened. It will be understood that the cams I'lassociated with these contact members may be suitably arranged to eiiect this desired operation.

As iliustrated in Fg. 4 of the drawings, the control motor CM is provided with an armature CMa and a separately excited field winding CEMI. 76

The direction of rotation of the armature CMa is eifected by reversing the polarity of the voltage applied theretoirom' the conductors Ll and L2 by means of a speed relay V.

, Before describing in detail the iunctioning of the control system illustrated in Fig. 4 of the drawings, the particular connections for the field windings of the regulator-generator R will be pointed out. It will be observed that the series field winding Rs is connected to be responsive to the current fiowing between the generator armature Ga and the motor armature Ma. The proportion of this current flowing through the series field winding Rs may be adjusted by means of a shunt S. The main field winding Ri of the regulator-generator R is connected to be responsive to the voltage which is applied to the motor armature Ma. In order to reduce the effect of the temperature rise of the main field winding Rr, due to the current flowing therethrough, it is connected in series circuit relation with a resistor 7-6 so that a principal `part of the voltage,

drop is consumed in the resistor, leaving the'balance tobe consumed in the main field winding Ri.. The differential field winding Rd of the regulator generator R is connected to be responsive to the current fiowing through the main generator field winding Gj and as illustrated, it may be connected in series circuit relation therewith. The differential field winding Rd and the main generator field winding Gj are arranged to be energized not only from the conductors Ll and L2, in accordance with the voltage obtained from the potentiometer Pl, but they are also arranged plied thereto a suitable control voltage, that the generator G and the regulator-generator R are being operated at the proper speed and that it is desired to move the elevator car o in the up direction. The operator then moves the master switch MS-to the up position to efiect the energization of the Operating winding of the up reversing switch U, as well as the energization of the Operating winding of the auxiliary switch X. The circuit for effecting the energization of these windings may be traced as follows:

Ll, MS, up contacts, FI, U, X, gate contact,

door contacts, Ll.

At contact members US a holding circuit-is prcvided around the mastenwitch MS. The brake winding Bw is released in response to the operation oi! the up reversing switch U. 4 The circuit for releasing the brake winding may be traced as follows:

Ll, Bw, UI, 1.2. I

The potentiometer PI is connected directly across the conductors Ll and L! on the closure o! contact members U! and U3 in'- response to the operation o! the up reversing switch U. Cur- -rentis then caused to flow through the main generator field winding Gj in part because of the voltage which is obtained from the first section of the potentiometer PI, due to the fact that contact members 'CI are closed, and partly because o! the voltage which is obtained !rom the armature Ra oi the regulator-generator R.

The Operating winding of the speed relay V is energized in response to the operation ot the up reversing switch U over a circuit which may be traced as tollows:

El, V, 1.2.

As a result of the energization of the speed relay V a circuit is completed for energizing the armature CMa of the control motor CM. This circuit may be traced as follows;-

p L, vl, cMa, v, co, L2.

The contact members Ci are then opened and the remaining contact members C2 through C'l are successively closed and opened, contact members C8 being closed but not opened, thereby increasing the voltage which is applied to the main generator field winding -Gf to correspondingly increase the voltage which is applied' to the armature Ma of the motor M. As soon as the contact members CID are opened, the armature CMa is deenergized and contact members cs remain closed.

The ifectiveness of the voltage which is obtained from the re'gulator generator armature Ra is increased on the closure of contact members V2 of the speed relay and the .opening of contact members VI; This change in the connections to the potentiometer PZ permits the regulator gen- As has been set forth hereinbefore, it is desirable that the speed of the motor M be at a certain value for each of the steps of control voltage obtained from the potentiometer PI. It is then possible to obtain a smooth acceleration curve which will be unaffected by the many variables in the system thathave been set forth in detail hereinbefore. In addition, it is also desired that the 'same speed relationship exist when the contact members CI through cs are operated in a reverse order to effect the deceleration of the motor M and the elevator car driven thereby.

I have found that the desired speed relationship will exist regardless of the variable characteristics of the elevator system when the regulator-generator R is employed and its field windings are connected as shown. Because of the connection .of the differential field winding Rd in series circuit relation with the main generator field winding Gj, the changes which are introdu'ced to effect a corrective action through the generator G are immediately reflected in the voltage which is -generated in the armature Ra. ot the regulator-generator. As a result, the corrective eifect which is applied by the regulatorgeneratcr R is in a sense proportional to the degree of variation in the speed of the motor M from the desired speed.

When it is desired to stop the elevator car at a particular floor, the operator centers the master switch, thereby completing a circuit for energizin'g the Operating winding of the slowdo'wninductor relay E. This circuit may be traced as 'follows:

Ll, MS, stop Contacts, E, XI, L2.

As soon as the contact members El come into proximity with the up inductor plate UE, they are opened and the previously traced energizing circuit ot the Operating winding speed relay V is opened. At contact members V3 a circuit is completed for connecting a field discharge resistor FD across the generator field winding Gi in order to permit .a less abrupt change in the 5 current flowing therethrough during the deceleration period. Since it is unnecessary to employ the maximum eflectiveness of the regula- 'tor generator R, the potentiometer PZ is again inserted in the circuit on the opening of contact members V2 and the closure of contact members VI.

The armature of the control motor CMa is energized in a reverse direction to eifect the operation of the contact members CI through cs in a reverse sequence. The circuit for now energizing the control motor armature CMa. may be traced as follows:

Ll, vs, CMa, V5, CS, L2.

- The contact members CT through C2 are successively closed and opened to eiect a decrease in the flow of current through' the main generator field winding 'Gf. During this interval,

the regulator generator R is -efiective to maintain the 'speed of the motor M at values corresponding to' the contact members which are closed. As a result, regardless of the variable conditions or loading of the 'elevator system, the elevator car lo will be decelerated at a unflorm rate.

A further result of the deenergization of the speed relay V is to close contact members vs and to complete an obvious energizing circuit for the Operating winding of the landing inductor relay F in parallel with the Operating winding of the slowdown inductor relay E. As soon as contact I opened, The breke B is then appliedand the' elevator car ID is broughtto rest at the desired floor. ,i

In order to further point out the application oi my invention, reference may be had in Fig. 5

of the drawings.-' The circuit connections there 5 shown are identical with those shown in Flg. 4, with the exception that the potentiometers PI and PI, the control motor CM, and the field discharge reslstor FD are omitted; Also, the connections for the armature Ra. of the regulator generator are somewhat altered and the speed relay V is arranged to short circult an aceelerating resistor Ar to per'nit the operation of the motor M at tull speed in one step. Since the regulator-generator R has a sufllcient range of 00 control to compensate for the IR drop in the armature of the. motor M and the generator G,

` the series field winding Gs may be omitted.

As shown on Fig. 5 of the drawings, the arma- 'ture Ra of the regulator-generator is connected across two of the opposite terminals of a ,wheat- 'stone bridge, one'leg of* which comprises the diflerntial field winding Rd of the re'gulatorgeneratonand the geld wlnding Gf o! the generator G. The remaining less ot the wheatstone'bridge comprise resistors rl, 1-2, andi-4. The opposite terminals of the Wheettone bridge not connected to the armature Ra are arrarged to be connected to the conductors Ll and L! and these connections may be'reversed by means of'the up and down reversing switches U and D.

A detailed description of the functioning and theory of operation of the Wheatstone bridge is set forth in the copending application of santini and myself, Serial No. 38,770 filed August 31, 1935, and assigned to the assignee of this application. r

Since the sequence of operation of the system shown in Fig. 5 of the drawings is somewhat similar to that set forth hereinbefore in connection with Flg. 4, only the portion necessary to illustrate the function of the Wheatstone bridge will now be set orth. As soon as the master switch MS is operated to the up position, for example, contact members U2 and U3 are closed to connect the Wheatstonebridge in series circuit relation wl'th the accelerating resistor. Ar and across the conductors Ll and L2. The breke winding Bw is energized and 'the motor M is then energized to move the elevator car in the up direction. The voltage which is applied to the main generator field winding Gj of the generator G is then a functionof the voltage existing, across the conductors Ll and L2, less the voltage which is consumed in the accelerating resistor Ar, and is further proportional to the voltage which is generated in the armature Ra of the regulator-generator. As is set forth in the copending application referred to hereinbefore, the voltage which is generated by the armature Ra may be independently applied to the generator field winding Gf and this effect will be entirely independent of the eflect which is caused by the voltage which is applied thereto from the source represented by the conductors Ll and L2.

When the speed relay V is energized, contact members VI are closed to short circuit the accelerating resistor Ar and the Wheatstone bridge circuit is' then-connected directly across the conductors Ll and LZ. The regulator-generator R.

' motor M will operate at a fixed speed regardless of the load or variable conditions affecting it.

Since certain further changes may be made in the oreg'oing construction and differentembodiments ot the invention may be made without departing from the scope thereof, it is intended that all matter shown in the accompanying drawings or set torth in the foregoing description shall be interpreted as illustrative and not in a limiting sense.

I claim as myinvention:

1. In a ward-leonard control system, in combination.- a first dynamo-electric device operatively connected to a load, a second dynamo-electric device electrically connectedto said first device, a field winding for said second device. a third dynamo-electrlcdevice disposed to be responsive to the current flowing between and the voltage across said first and second devices for controlling the current flowing through said field winding, and a field winding in said third device conp nected to be responsive to the current flowlng 'through said flrst-mentioned field winding !or opposing' the tunctioning of said third device in to changes in the current flowingbetween and the voltage across said first and second devices.

2 In award-Leonard control system, in combination, a first dynamo-electric device operatively connected to a load, a second dynamo-electric device electrlcally connected to said first device. a main field win l for' said second device, a third dynamo-electric device tor controlling the current flowing through 'said main field windaoeasio ing, said third device being provided with series and shunt fleld windings' disposed respectively to be responsive to the current fiowing between and the voltage across said first and second devices, and means responsive to changes' caused in said main fleld winding in response to changes in current flow through said series and shunt field windings for effecting a further control of the functioning of said third device.

3. In a ward-Leonard control system, in combination, a. first dynamo-electric device operatively connected to a load, a second dynamo-'electric device electrically connected' to said first device, a main field winding for said second device, a third dynamo-electric device for controlling the current flowing through said main field winding, said third device being provided with series and shunt field windings disposed respectively to be responsive to the current flowing between and the voltage across said flrst and second devices, and means responsive to changes in current flow through said main fleld winding in response to changes in current flo w through said series and shunt field windings for opposing the functioning of said third device in further changing the current flowing throughsaid field winding. I

4. In a ward-Leonard control system, in combination, a flrst dynamo-electric device operatively connected to a load, a second dynamo-electric device electrically connected to said first device, a main field winding for said second device, a third dynamo-electric device for controlling the current flowing through said main fleld winding, said third device being provided with series and shunt field windings disposed respectively to be responsive to the current flowing between and the voltage across said first and second devices, and a differential field winding in said third device connected to be responsive to the current flowing through said main field winding for opposing the functioning of said third device in response to changes in flow of current through said series and shunt fleld windings.

5. In a ward-Leonard control system, in combination, a first dynamo-electric device operatively connected to a load, a second dynamo-electric device eiectrically connected 'to said first device, a, main field winding for said second device, a third dynamo-eiectric device for controlling the current flowing through said main fleld winding, said third device being provided with series and shunt fleld windings disposed respectively to be responsive to`the current flowing between and' the voltage across said first and second devices, said series and shunt field windingsbeing differentially related to provide a resultant flux substantially proportional tothe speed of said first device, and means responsive to the changes caused in said main field winding in response to changes in current flow through said series and shunt -fleld windings for eifecting a further control of the functioning or said third device. i

6. In a ward-Leonard control system, in com.- bination, a. first dynamo-electric device operativeiy connected to a load, a second dynamo-electric device electrically connected to said first device, a main field winding for said second device, a third dynamo-electric device for controllin'g the current flowing through said main field winding, said third device being provided with series and shunt field wlndings' disposed respecbe responsive to the current flowing and the voltage across said first and tively to between ing in said third device connected to be responsive to the current` flowingthrough said main field winding and differentially related to said shunt fleld winding for opposing the functioning of said third device in response to changes in flow of current through said series and shunt field windings.

7. In a Ward-Leonard controlsystem, in combination, a motor operatively connected to a load device, a main generator disposed to energize said motor, a separately excited -fleld winding for said main generator, and an auxiliary generator for controlling the flow of current through said field winding and provided with a series field winding, a main field winding and a differential fleld winding, said series field winding being disposed to be responsive to the current flow to said motor from said generator, said main field winding being' disposed to be responsive to the voltage applied to said motor by said main generator; and said difierential field winding being connected 'in series circuit relation with said separately excited field winding.

8. In a ward-Leonard control system, in combination, a motor operatively connected to a load device, a main generator disposed to energize said motor, a main field winding for said generator, and an auxiliary generator having an armature connected in series circuit relation with said main field winding, said auxiliary generator .being provided with series and shunt field windings disposed respectively to be responsive to the current flowing between and the voltage across said motor and said main generator, and means responsive to changes caused in said main field winding in response to changes in current flow through said series and shunt fleld windings for efiecting a further control of the functioning of said auxiliary generator.

9. In a ward-Leonard control system, in combination, a motor operatively connected to a load device, a main generator' disposed to energize said motor,a main field winding for said generator, and a regulator-generator having an armature connected in series circuit relation with said main fleld winding, said regulator-generator being provided with series and shunt field windings disposed respectively to be responsive to the current flowing between andthe voltage across said motor and said main generator', and means responsive to changes in current flow through said mainfleld winding in response to changes in current flow through said series and shunt field windings for opposing the functioning of said flowing between and the voltage across said' motor and said main'generator, and a diflerential field winding in said regulator-generator connected in series circuit relation with said main field winding !or op'posing the tunctoning of current fiowing between and the voltage across said motor and said main generator, said series and shunt field windings being difi'erentialiy re'- lated to effect the generation in sa d armature of a voltage substantially proportional to the speed of said motor, and means responsive to the changes caused in said main'field winding in response to changes in current flow through' said series and shunt field windings for effecting a further control of the functioning of said regulator-generator.

12. In a ward-Leonard control system, in combination; a motor operatively connected to a load device, a main generator disposed to energize said motor, a main field winding for said generator, and' a regulator-generator having an armature connected-in series circuit relation wlth said main field winding, said regulator-generator being provided with series and shunt field windings dis-v posed respectively to be responsive to the current fiowing between and the voltage across said motor and said main generator, said series and shunt field windings being differentially related to efiect* the 'generation in said armature of a voltage substantially proportional to the speed of said motor, and a third field winding in said regulatorgenerator connected in series circuit with said 40 main field winding and diiTerentially related to said shunt field winding for generating a voltage in said armature ,in opposition to the voltage generated therein by the resultant efiect of said series and shunt field windings.

13. In a direct-current motor control'system, a rstdynamo-electric machine having an arma i ture, a second dynamo-electric machine having an -armature-serially connected with said first-mentioned 'armature and having a. field winding, one 0 ot said machines being driven at substantially constant speed 'with variable excitation and the other of said machines being operated as a motor %at variable speed, a third dynamo-electric machine .having an armature connected tosaid field winding to vary the voltage applied thereto, said third machine having a separate excitation winding, an excitation circuit connecting said field winding and said separate excitation winding directly 'in series whereby the current flow in said oo windings is the same at any instant reg'ardless of the relative time constants of said windings,

and additional excitation means for said third machine for supplying a component of excitation thereto substantially proportional to the speed of said machine operated as a moter, said additional excitation means normally acting in opposition to said separate excitation winding whereby said third machine is difierentially excited in accordance with the speed'of said 'machine operated as a motor and the current in said excitation circuit.

14. In a direct-current motor control system, a first dynamo-electric machine having an arma.- ture, a second dynamo-electric machine having an armature serially connected With said first mentioned armature and having a field winding, one of said machines being driven at substantially constant 'speed with variable' excitaton and the otherof said machines being operated as a motor at variable speed, a third dynamo-electrlc machine 'having an armature connected to said field winding to vary the voltage applied thereto, a separate excitation winding, a shunt type winding connected to respond to the voltageacross one of said serially connected armatures, and a ,series type winding connected to respond to' the current in said serially connected armatures, and an excitation circuit' connecting said field winding and said separate excitation winding directly in series, whereby the current in said field winding and said' separate 'excitation winding is the same at any instant, regardless of the relative time constants of the latter windings.

` 15. In a motor control system of the Ward- Leonard type, a motor having an armature, a

generator having an armature connected in a loop circuit with said first-mentioned armature and having a generator field winding, said generator being driven' at substantially constant speed with variable excitation and said motor being operated at variable speed, an auxiliary generator having an armature connected to said generator field winding to vary the voltage applied thereto a separate excitation winding, a shunttype winding connected to respond to the voltage i i 'across one of said serially connected armatures,

and a series type winding connected to respond to the current in said loop circuit, and an excitation circuitconnecting saidgenerator field winding and said separate excitation winding directly in series, said separate excitaton and sh nt type. windings being connected' to produce normally opposing magnetomotive forces in said the voltage losses in said loop circuit caused by resistance.

KENNETHM.WHI'IE.' 

